Directly to the point: Since months ago, I noticed that CDDA doesn't play with USA 1.10 BIOS, only after going to the BIOS setup settings; if the BIOS sequence is inmediately skipped, it works entirely normal.

With JAP BIOS, the CDDA simply doesn't play (though the LED keeps turned on)

I have absolutely no clue about what is really happening, since I do exactly what the manual/macros states.

If you wonder why I'm using the communication registers for everything, the code is from my Wolf32X mode 1 source. The MD side is controlling the CD side through the comm regs, getting info back through the comm registers. If you are using this all on the CD side, just use global vars in ram instead of the comm regs.

You're welcome. I had to work that out myself when doing the CDDA support for Wolf32X, and I'm always happy to share coding tips. If you need tips on reading data sectors and handling ISO9660, I've got that, too.